Read the Stereophile Review in their Archives at www.stereophile.com . They cover both versions in their review.
While I would go with the 20 amp version over the 15 amp, get the 15 amp IEC with it instead of the 20 amp. PS Audio tells me the 15 amp outlet is capable of about 40 amps, so will allow the 20 amp Ultimate Outlet to fully function, yet be far more compatible with the majority of power cords.
Jeff Delman
Value Audio